Lubrication for refrigerant heat transfer fluids

Abstract

Esters and mixtures of esters of polyhydric alcohols, e.g., of pentaerythritol, in which at least 22 number percent of the acyl groups in the esters are either branched or contain no more than six carbon atoms, are effective lubricants and/or lubricant base stocks for chlorine-free fluorocarbon refrigerant heat transfer fluids, particularly for chlorine-free heat transfer fluids such as Refrigerant 134a (1,1,1,2-tetrafluoroethane).

What is claimed is: 
     
       1. A refrigerant working fluid comprising: (A) a fluoro-group-containing heat transfer fluid; and   (B) a lubricant composition consisting essentially of materials selected from the group consisting of esters of (i) alcohols containing at least two --OH groups and (ii) organic carboxylic acids, wherein: (a) at least about 22 number percent of the acyl groups in the total of all the esters in said lubricant composition include no more than six carbon atoms, or include at least one carbon atom bonded to at least three other carbon atoms by single bonds, or both;   (b) the ratio of the number percent of acyl groups in the total of all the esters in said lubricant composition that are that contain 8 or more carbon atoms and are unbranched to the number percent of acyl groups in the total of all the esters in said lubricant composition that are both branched and contain not more than 6 carbon atoms is not greater than about 1.56;   (c) the number percent of acyl groups in the total of all the esters in said lubricant composition that contain nine or more carbon atoms is not greater than about 81; and   (d) at least 62 number percent of the total of all the alcohol moieties in the esters in said lubricant composition contain at least one carbon atom that is bonded by carbon-carbon single bonds to four other carbon atoms.     
     
     
       2. A refrigerant working fluid according to claim 1, wherein: (a) at least 81number percent of the total of all the alcohol moieties in the esters in said lubricant composition contain at least one carbon atom that is bonded by carbon-carbon single bonds to four other carbon atoms;   (b) the ratio of the number of monovalent acyl groups to the number of acyl groups with more than one valence in the total of all the esters in said lubricant composition is at least 1.76; and   (c) the number percent of acyl groups containing at least nine carbon atoms in the total of all the esters in said lubricant composition is not greater than 67.   
     
     
       3. A refrigerant working fluid according to claim 2, wherein: (a) at least 81 number percent of the total of all the alcohol moieties in the esters in said lubricant composition are moieties derived from the group consisting of pentaerythritol, dipentaerythritol, and 2,2-dimethylol-1butanol;   (b) the ratio of the number of monovalent acyl groups to the number of divalent acyl groups in said lubricant composition is at least about 4, and there is not more than 2 number percent of acyl groups with a valence higher than 2;   (c) the number percent of acyl groups containing at least nine carbon atoms in the total of all the esters in said lubricant composition is not greater than 45; and   (d) the number percent of total oxygen atoms in the total of all the esters in said lubricant composition that are chemically bonded to hydrogen is not greater than 5.   
     
     
       4. A refrigerant working fluid according to claim 1, wherein: (A) at least 22 number percent of the total number of acyl groups in all the esters of all alcohols containing at least two --OH groups present in the lubricant composition are selected from the group consisting of (i) acyl groups containing no more than 5 carbon atoms and (ii) acyl groups containing at least one carbon atom bonded to at least three other carbon atoms by single bonds; and   (B) at least 12 number percent of the acyl groups in the esters of all alcohols containing at least two --OH groups present in the lubricant composition contain at least 8 carbon atoms each.   
     
     
       5. A refrigerant working fluid according to claim 4, wherein: (A) at least 50 number percent of total number of acyl groups in all the esters of all alcohols containing at least two --OH groups present in the lubricant composition are selected from the group consisting of (i) acyl groups containing no more than 5 carbon atoms and (ii) acyl groups containing at least one carbon atom bonded to at least three other carbon atoms by single bonds;   (B) at least 21 number percent of the acyl groups in the esters of all alcohols containing at least two --OH groups present in the lubricant composition contain at least 9 carbon atoms each; and   (C) at least 81 number percent of all the alcohol moieties in the esters of all alcohols containing at least two --OH groups present in the composition are moieties derived from alcohols that contain at least one carbon atom bonded to four other carbon atoms by carbon-carbon single bonds.   
     
     
       6. A refrigerant working fluid according to claim 5, wherein: (A) at least 14 number percent of total number of acyl groups in all the esters of all alcohols containing at least two --OH groups present in the lubricant composition are selected from 3-methyl butanoyl and 2-methyl butanoyl groups; and   (B) at least 81 number percent of all the alcohol moieties in the esters of all alcohols containing at least two --OH groups present in the lubricant composition are moieties derived from alcohols selected from the group consisting of pentaerythritol, dipentaerythritol, and 2,2-dimethylol-1-butanol.   
     
     
       7. A refrigerant working fluid according to claim 6, wherein said fluoro-group-containing heat transfer fluid is chlorine-free. 
     
     
       8. A refrigerant working fluid according to claim 5, wherein said fluoro-group-containing heat transfer fluid is chlorine-free. 
     
     
       9. A refrigerant working fluid according to claim 4, wherein said fluoro-group-containing heat transfer fluid is chlorine-free. 
     
     
       10. A refrigerant working fluid according to claim 3, wherein said fluoro-group-containing heat transfer fluid is chlorine-free. 
     
     
       11. A refrigerant working fluid according to claim 2, wherein said fluoro-group-containing heat transfer fluid is chlorine-free. 
     
     
       12. A refrigerant working fluid according to claim 1, wherein said fluoro-group-containing heat transfer fluid is chlorine-free. 
     
     
       13. A refrigerant working fluid according to claim 1, which has only a single phase at equilibrium over a temperature range from about -40° C. to about 100° C. 
     
     
       14. A process for operating a mechanical refrigerating system comprising cyclic compression, liquefaction, expansion, and evaporation of a fluoro-group-containing heat transfer fluid, wherein the improvement comprises lubricating a part of the refrigerating system that comes into contact with the heat transfer fluid with a lubricant composition consisting essentially of materials selected from the group consisting of esters of (i) alcohols containing at least two --OH groups and (ii) organic carboxylic acids, wherein: (A) at least about 22 number percent of the acyl groups in the total of all the esters in said lubricant composition include no more than six carbon atoms, or include at least one carbon atom bonded to at least three other carbon atoms by single bonds, or both;   (B) the ratio of the number percent of acyl groups in the total of all the esters in said lubricant composition that contain 8 or more carbon atoms and are unbranched to the number percent of acyl groups in the total of all the esters in said lubricant composition that are both branched and contain not more than six carbon is not greater than about 1.56;   (C) the number percent of acyl groups in the total of all the esters in said lubricant composition that contain nine or more carbon atoms is not greater than about 81; and at least 62 number percent of the total of all the alcohol moieties in the esters in said lubricant composition contain at least one carbon atom that is bonded by carbon-carbon single bonds to four carbon atoms.   
     
     
       15. A process according to claim 14, wherein in said lubricant composition: (a) at least 81 number percent of the total of all the alcohol moieties in the esters in said primary lubricant component contain at least one carbon atom that is bonded by carbon-carbon single bonds to four other carbon atoms;   (b) the ratio of the number of monovalent acyl groups to the number of acyl groups with more than one valence in the total of all the esters in said primary lubricant component is at least 1.76; and   (c) the number percent of acyl groups containing at least nine carbon atoms in the total of all the esters in said primary lubricant component is not greater than about 67.   
     
     
       16. A process according to claim 15, wherein in said lubricant composition: (a) at least about 81 number percent of the total of all the alcohol moieties in the esters in said primary lubricant component are moieties derived from the group consisting of pentaerythritol, dipentaerythritol, and 2,2-dimethylol-1-butanol;   (b) the ratio of the number of monovalent acyl groups to the number of divalent acyl groups in said primary lubricant component is at least about 4, and there is not more than 2 number percent of acyl groups with a valence higher than 2;   (c) the number percent of acyl groups containing at least nine carbon atoms in the total of all the esters in said primary lubricant component is not greater than 45; and   (d) the number percent of total oxygen atoms in the total of all the esters in said primary lubricant component that are chemically bonded to hydrogen is not greater than 5.   
     
     
       17. A process according to claim 14, wherein said lubricant composition comprises at least two esters that are esters of an alcohol containing at least two --OH groups, and: (A) at least 22 number percent of total number of acyl groups in all the esters of all alcohols containing at least two --OH groups present in said lubricant composition are selected from the group consisting of (i) acyl groups containing no more than 5 carbon atoms and (ii) acyl groups containing at least one carbon atom bonded to at least three other carbon atoms by single bonds; and   (B) at least 12 number percent of the acyl groups in the esters of all alcohols containing at least two --OH groups present in said lubricant composition contain at least 8 carbon atoms each.   
     
     
       18. A process according to claim 17, wherein: (A) at least 50 number percent of total number of acyl groups in all the esters of all alcohols containing at least two --OH groups present in said lubricant composition are selected from the group consisting of (i) acyl groups containing no more than 5 carbon atoms and (ii) acyl groups containing at least one carbon atom bonded to at least three other carbon atoms by single bonds;   (B) at least 21 number percent of the acyl groups in the esters of all alcohols containing at least two --OH groups present in said lubricant composition contain at least 9 carbon atoms each; and   (C) at least 81 number percent of all the alcohol moieties in the esters of all alcohols containing at least two --OH groups present in said lubricant composition are moieties derived from alcohols that contain at least one carbon atom bonded to four other carbon atoms by carbon-carbon single bonds.   
     
     
       19. A process according to claim 18, wherein: (A) at least 14 number percent of total number of acyl groups in all the esters of all alcohols containing at least two --OH groups present in said lubricant composition are selected from 3-methyl butanoyl and 2-methyl butanoyl groups; and   (B) at least 81 number percent of all the alcohol moieties in the esters of all alcohols containing at least two --OH groups present in said lubricant composition are moieties derived from alcohols selected from the group consisting of pentaerythritol, dipentaerythritol, and 2,2-dimethylol-1-butanol.   
     
     
       20. A process according to claim 14, wherein no more than 9 number percent of the oxygen atoms in the total of all the esters in said lubricant composition are chemically bonded to hydrogen atoms.